Calendar watches are usually arranged to indicate the values appropriate to a solar calendar, more particularly the Julian calendar or the Gregorian calendar. The calendar mechanism is essentially arranged to count the number of days appropriate to each month and when applicable to count the months and to increment a year counter every twelve months. This mechanism is thus simply actuated once per day by the timepiece movement, by means of a wheel driven by the hour wheel with a ratio of 1:2.
The present invention proposes to incorporate calendar indicator members for the traditional Chinese calendar into a timepiece. Nowadays, the Chinese calendar is still used to set the date of some festivals and for Chinese astrology. This calendar is very different from western ones because it is mainly based on the synodic months, whose mean duration is not equal to an integral number of days. The known mechanisms for displaying the values of the Julian calendar or other solar calendars accordingly cannot be used for this purpose.
The Chinese calendar is of the lunar-solar type, in the sense that it is based on the lunar months which correspond to the synodic months, while the Chinese years have a variable duration in order to approximate tropical years as far as possible, i.e. the apparent movement of the sun at the ecliptic. This calendar comprises a cycle of nineteen years, called the Chang cycle, which comprises as near as can be an integral number of lunar months (235) and of tropical and Chinese years (19) and whose beginning is set in such a manner as to satisfy the historical requirement fixing the Chinese New Year at the second new moon which follows the winter solstice, apart from rare exceptions. Each of these periods of nineteen Chinese years comprises twelve ordinary years of twelve lunar months and seven years called leap years of thirteen lunar months. If the years in the Chang cycle are numbered, the leap years typically have the numbers 1, 4, 7, 10, 12, 15 and 18. These years comprise a supplementary lunar month also having the duration of a synodic month, which is called a “leap month”. This month is intercalated between two of the ordinary months at a non cyclic position which depends on astronomical data and which thus varies from one leap year to another. The lunar months which follow it keep the same name or number as in an ordinary year. Depending on the time of the new moon on each involved New Year's Day, an ordinary year of the Chinese calendar can comprise 353, 354 or 366 days while a leap year can comprise 383, 384 or 385 days.
For more information regarding the Chinese calendar the reader can refer to the publication of Nachum DERSHOWITZ and Edward M. REINGOLD, Calendrical Calculations, Cambridge University Press, 1997; also the publications or Helmer ASLAKSEN: The Mathematics of the Chinese Calendar, 13 May 2004 and LeapMonths.nb, Mathematica package 1999 available on the site www.math.nus.edu.sg. We will only mention here that the Chinese years are not identified by a number but by a name formed by the combination of two terms comprising a heavenly stem and a earthly branch. There are ten earthly stems, each formed by association of one of five elements (wood, fire, earth, metal, water) with the term “Yang”, then with the term “Yin” the following year, which gives a cycle of ten years. Moreover there are twelve earthly branches carrying the names of animals of twelve constellations of the Chinese zodiac, which are traversed in twelve years by Jupiter. Through the combination of two cycles of ten and twelve years, the names of the Chinese years repeat with a cycle of sixty years.